Glow discharge lamp



y L. GQLDSTEIN ETAL 2,374,677

' GLOW DISCHARGE LAMP Filed Sept. 20, 1943 MMM ATTORNEY$ Patented May 1,1 945 GLOW DISCHARGE LAMP Ladislas Goldstein and Francis Perrin, NewYork, N. Y., assignors to Canadian Radium &

Uranium Corporation poration oi New York New York, N. Y., a cor-Application September 20,1943, Serial No. 503,046 W '3 Claims. (Cl.176-122) Our invention relates to a new and improved gas-containingdischarge lamp, of the'type which is designated as a glow lamp or a glowtube. Such lamps are also designated as cold electrode lamps, becausethe electrodes of such lamps remain unheated save by the very moderateheat which is developed by the discharge itself.

Such lamps are intended for operation under a predetermined operatingvoltage. In order to start or to strikesuch a lamp, it is necessary toapply a striking voltage which exceeds said operating voltage; In thecircuit in which such a lamp is located, it is necessary to apply anovervoltage, which exceeds the striking voltage. This is done in orderto suppress or minimize the delay in starting the lamp.

For example, inthe type of lamp which is specifically described herein,as. one example of our invention, the striking voltage can vary from 70volts to 90 volts and the operating voltage is about 15 volts less thanthe striking voltage. The over-voltage which is applied to the lamp inorder to start the same promptly. exceeds the striking voltage by about5 volts.

Experience has shown that the striking voltage can vary greatly,depending upon the length of time in which the lamp has been shieldedfrom.

light. For many uses, it is necessary to locate the lamp in a hood orcasing which shields the lamp from externallight, so that the lampcanremain unexposed to light for long and varying periods of time. Theperiod during which the lamp remains inoperative is designated as theidle period." The striking voltage varies greatly with the length ofsaid idle period, when the lamp is struck for the first time after suchidle period, if the lamp is shielded from external light during suchidle period. Such idle period is designated as a shielded idleperid,.during which the lamp is shielded from external light.

In certain uses, the idle period can'beas long as one or two days,during which period the lamp is shielded from light. Under suchcircumstances, there can be a variation in the striking voltage of asmuch as 50%, in the first striking after such shielded. idle period.,Hence, ii'the circuit is designed so as to supply a'normal overvoltagewhich exceeds the striking voltage by only volts,'the starting ot-thelamp can be greatly delayed, and such starting may not take place. inthe first attempted striking after such shielded idle period, thusproducing great unce'r-' tainty in operation, because the necessarystrikin: voltage itself may greatlyexceed even the over-voltage which isapplied to the lamp by the circuit, when it is desired to start the lampafter such shielded idle period.

According to our invention, we continuously irradiate the interior ofthe lamp, including its internal electrodes as well as its internalwall, by

means of a source of light which is independent of the circuit of thelamp. For example, this independent irradiation can be produced by meansof a. phosphorescent or fluorescent mate,-

rial, such as phosphorescent zinc sulfide, intermixed with radiumbromide or other radioactive material which emits alpha rays. Suchmixture continuously produces light which sufliciently irradiates theglow lamp, so that the variation of the striking voltage in the firststriking after a shielded idle period islimited to less than as comparedwith the present usual variation of about 50% or more.

radiation, we can reduce the variation in the.

By supplying sufflcient irrequired striking voltage after such shieldedidle period to much less'than 10%, to as low as 5% or even less.

Another object of our invention is to provide an irradiation, wholly ormainly in those wave lengths to which the electrodes are sensitive.These wavelengths will depend upon the material of the electrodes, andit will also depend upon whether the electrodes are coatedpr uncoated.In many cases, the cold electrodes are coated with a material whichemits electrons readily, and under the application of low energy. Thesematerials aredesignated as "low work-function sub- I stances. Examplesof such low work-function substances are caesium oxide, barium oxide andother materials-which are well known for this -bodiment. of ourinvention.

Our invention is described with reference to 'a If the lamp has suchcoated electrodes, visible light may be used to irradiate the bulb.However, even in this case, the violet and ultra-violet light will bemore eflicient. By selecting from the well-known luminescent materials,which include phosphorescent andfluorescent materials, we can secureradiated light of various colors, thusselecting a range of wave lengthwhich ,willhave the maximum photoelectric eil'ect.

Other important objects of our invention will be stated in the'annexeddescription and single diagrammatic drawing, which illustrate anemstandard commercial lamp, which has a g ass bulb or envelope I, whoseheight is about 20 millimeters. This is provided with spaced coldelectrodes 2 and 3 which are made of nickel. Said envelope l'has agaseous filling whose pressure at V normal temperature of about 20#c.-25 C. is about 20 millimeters of mercury. This filling consists of99% of neon and 1% of argon. Each Of the electrodes 2 and 3 is a solidmetal cylinder.

' The height of each cylinder is 12 millimeters, and its diameter is lmillimeter. stated herein as an illustration, the electrodes 2 .and 3are equal and parallel to each other. The

In the example width of the space between said electrodesis about 2-3millimeters. The internal wall of the envelope is substantiallycylindrical and the diameter of such internal wall is about millimeters.

Since commercial lamps of this type willvary from lamp to lamp, due toinaccuracies in commercial manufacture, the striking voltage can varyfrom lamp to lamp from about 70 volts to 90 volts, and possibly more.One th'eaverage, the operating voltage is 15 volts less than thestriking voltage. The over-voltage which is applied in order tostrikethe'lamp without undue delay, exceeds the striking voltage by about 5volts. This is stated by way of illustration, because the importantfactor herein is to provide a uniform' striking voltage so that saidstriking voltage is stabilized, with a variation which is insignificantfor practical purposes.

The improved lamps can be used in switches, relays, transmittingpictures by wire or radio, and for many other purposes, inwhich a stablestriking-voltage is required.

After a lamp of this type has had an idle period of one or two days,during which idle period the lamp is shielded from light, the strikingvoltage for the particular lamp may increase by as much as 50%. Afterthe lamp has been struck for the first time after a lon shielded idleperiod, its striking voltage during subsequent strikings will have-onlya much smaller value, if the intermediateshielded idle.

period is very short. Therefore, an important feature of our inventionis to stabilize thestriking voltage, even if the lamp has been shieldedfrom light during a-long idle period. A long idle period can vary fromten minutes to one or two days, or even more.

A suitable self-luminescent composition can be made, for example, byintermixing with 1 gram of fluorescent zinc sulfide, 100-130 micromideor other suitable radium salt. v

When we refer'to this masS l00-l30 micrograms of radium, we refer to themass of the radium in the radium bromide, so that the massof the radiumbromide itself will exceed 100-130 micrograms. A self-luminescentcomposition of this type will produce a luminescense. of approximately100 micro-lamberts.

- luminescent material can be applied to the inis therefore unnecessaryto describe the specific mode of applying the self-luminescentcomposition, either'to the interior or exterior wall of the bulb L; Thecomposition is preferably applied over the entire internal wall, or overthe entire external wall of the bulb I, but our invention is not limitedthereto. Said composition may be applied to one or more spots, either tosaid. internalwall or to saidexternal wall. The composition ispreferably not applied to the electrodes 2 and 3.

The photoelectric eflect of an illumination of about 100 micro-lambertsis sumcient to supply enough photons, so that according'to our theory,there will also be sufilcient free electrons in the gaseous filling ofthe lampin order to stabilize the striking voltage. Likewise, someionization may be',produced by the alpha'and beta, rays which areemitted by the radium, but I our invention is particularly directed tothe photoelectric eilfect.

On the other hand, if the coating would consist of zinc sulfide or otherphosphorescent material alone, such coating would not stabilize .thestriking voltage after a substantial shielded idle period.

In additionto making the walls of such tubes of glass or. i otlierlight-permeable material, it is well known;- make such walls of metal orother material whichvis impermeable to light. In. such case, we locatethe self-luminescent ma terial in'the interior of the bulb. The selfnersurface of the glass or metal bulb, or to the material, or to anysuitable carrier which is located within the bulb. Said carrier may befixed to the interior wall of the'bulb. For example, such carrier may bea rod of glass or 40 the like, which is fixed to the interior wall of pthe bulb. In eifect, such a carrier would be an, extension of theinterior wall of the bulb.

Likewise, if the self-luminescent material is external to the wall ofthe bulb, such selfluminescent material may be mounted upon a Such acomposition canbe applied either to I the internal wall or to-theexternal wall of the envelope I. The wall of the'envelope I can be madeof material which is permeable to ultra violet rays. There are wllknowntypes of glass which are permeable to ultra-violet rays, and we can usesuch wellknown glass compositions.

'However, the invention is not limited topthe use of ultra-violet rays,and it may be that ultra-violet rays are not emitted by theacti-- vatedfluorescent zinc sulfide.

It is well known to apply such compositions to a glass wall. or thelike, by incorporating such compositions in suitable transparentvarnishes or lacquers which are optionally but not necessarily,permeable tothe ultra-violet rays, as

well'as to the rays in the visible spectrum. It

' grams of radium, in the formpf radium brocent material does not affectthis normal discharge current under the same conditions of voltage andexternal resistance.

The weight of the radium which is.utilized in I the self-luminescentmaterial for. the specific lamp described herein, may vary from about 2micrograms to 20 micrograms. When'we refer to a "glow discharge, werefer to a discharge in which-the discharge current is less than in thearc discharge or in the spark discharge. In order to maintain the glowdischarge between cold electrodes, and in order to prevent suchdischarge from becoming an arc discharge or a spark discharge, we limitthe discharge cur- ,rent by suitable external resistances. The coldelectrodes 2 and 3 have substantially'no disinte- 7 gration in the glowdischarge. Such electrodes inner surface of a bulb made of any suitableherein, having a, striking voltage which varies more than 10% forstriking said lamp initiallyhave a high rate of disintegration in asustaining arc discharge or spark discharge, v

' We are concerned primarily with the starting of the lamp. After thelamp has' been started by the discharge between cold electrodes, theintensity of the discharge current may exceedthe intensity of the glowdischarge, so that the lamp may operate, after starting, at glowdischarge or arc discharge or spark discharge. For some uses,

able gaseous filling and spaced cold electrodes,

said lamp, when not irradiated as later specified discharge,

after a light-shielded idle period of m'ore'than ten minutes, said lamphaving a source of light 'rays associated therewith, said surcedelivering light rays to the interior of said lamp, said sourcecomprising radioactive material and additional material which isactivated by said radioactive material to emit said light rays, saidsource delivering a substantially'uniform supply of light rays, saidsupply being sufllcient to make said striking voltagein said initialstriking uniform within a range of less than 10%.

2.,A glow discharge lamp according to claim'l, in which said source isfixed to said lamp.

. '3. A glow discharge lamp according to claim 1, in which said. sourceis fixed to said'lamp, and said source is spaced from said electrodes.

LADIsLAs GOLDSTEIN. FRANCIS PERRIN.

